The semiconductor industry is currently considering the use of thin films of various metals for a variety of applications. Many organometallic complexes have been evaluated as potential precursors for the formation of these thin films. A need exists in the industry for developing new compounds and for exploring their potential as precursors for film depositions. The industry movement from physical vapor deposition (PVD) to chemical vapor deposition (CVD) and atomic layer deposition (ALD) processes, due to the increased demand for higher uniformity and conformality in thin films, has lead to a demand for suitable precursors for future semiconductor materials.
In the industry, conducting metals such as copper are being used to fill sub-micron features on substrates during the manufacture of integrated circuits. However, copper can diffuse into the structure of adjacent dielectric layers, thereby compromising the integrity of the devices being formed. Diffusion, as well as interlayer defects, such as layer delamination, may be prevented by depositing a barrier layer, a liner layer, or a combination of both, on the underlying material before depositing the conducting metal. The barrier layer is deposited on the underlying material and is often a nitride of a metal that prevents interlayer diffusion and minimizes chemical reactions between underlying materials and subsequently deposited materials. The liner layer is conventionally composed of a metal that provides adhesion for the conducting metal layer.
Metals such as tantalum, niobium, tungsten, and the respective metal nitrides are being considered for liner and barrier materials in copper applications. See, for example, U.S. Pat. Nos. 6,491,978 B1 and 6,379,748 B1. Depending on the application, a liner adhesion layer and/or a diffusion barrier layer may comprise a metal, such as tantalum, niobium, or tungsten, a metal nitride layer, such as tantalum nitride, niobium nitride layer, or tungsten nitride, a metal and metal nitride stack, or other combinations of diffusion barrier materials. Metal and metal nitride layers have been traditionally deposited by PVD techniques. However, traditional PVD techniques are not well suited for providing conformal coverage on the wall and bottom surfaces of high aspect ratio vias and other features. Therefore, as aspect ratios increase and device features shrink, new precursors and deposition techniques are being investigated to provide conformal coverage in these device features.
As referred to above, one proposed alternative to PVD techniques of metal and metal nitride layers is depositing the layers by CVD techniques to provide good conformal coverage of substrate features. The ability to deposit conformal metal and metal nitride layers in high aspect ratio features by the disassociation of organometallic precursors has gained interest in recent years due to the development of CVD techniques. In such techniques, an organometallic precursor comprising a metal component and organic component is introduced into a processing chamber and disassociates to deposit the metal component on a substrate while the organic portion of the precursor is exhausted from the chamber.
There are few commercially available organometallic precursors for the deposition of metal layers, such as tantalum, niobium, and tungsten precursors by CVD techniques. The precursors that are available produce layers which may have unacceptable levels of contaminants such as carbon and oxygen, and have less than desirable diffusion resistance, low thermal stability, and undesirable layer characteristics. Further, in some cases, the available precursors used to deposit metal nitride layers produce layers with high resistivity, and in some cases, produce layers that are insulative.
Another proposed alternative to PVD processes is ALD processes. ALD technology is considered superior to PVD technology in depositing thin films. However, the challenge for ALD technology is availability of suitable precursors. ALD deposition process involves a sequence of steps. The steps include 1) adsorption of precursors on the surface of substrate; 2) purging off excess precursor molecules in gas phase; 3) introducing reactants to react with precursor on the substrate surface; and 4) purging off excess reactant.
For ALD processes, the precursor should meet stringent requirements. First, the ALD precursors should be able to form a monolayer on the substrate surface either through physisorption or chemisorption under the deposition conditions. Second, the adsorbed precursor should be stable enough to prevent premature decomposition on the surface to result in high impurity levels. Third, the adsorbed molecule should be reactive enough to interact with reactants to leave a pure phase of the desirable material on the surface at relatively low temperature.
As with CVD, there are few commercially available organometallic precursors for the deposition of metal layers, such as tantalum, niobium, and tungsten precursors by ALD techniques. ALD precursors that are available may have one or more of following disadvantages: 1) low vapor pressure, 2) wrong phase of the deposited material, and 3) high carbon incorporation in the film.
Therefore, there remains a need for developing new compounds and for exploring their potential as CVD and ALD precursors for film depositions. There also remains a need for a process for forming liner and/or barrier layers of metal or metal derivative materials from organometallic precursors using CVD and ALD techniques. Ideally, the liner and/or barrier layers deposited are substantially free of contaminants, have reduced layer resistivities, improved interlayer adhesion, improved diffusion resistance, and improved thermal stability over those produced with PVD processes.